Paying to decrypt ransomed data seems bonkers too. You’re going to trust they didn’t change something during the encrypt/decrypt process (even if by accident like a bug)? Do people that pay the ransom do something to mitigate this risk?
They could very well have changed something on purpose before encrypting, but they do have a reputation to uphold if they want to keep getting “customers”. At least in the high profile cases, the ransomers do seem to be honest and dependable if they are paid.